Biocidal self-adhesive and process for producing the same, as well as self-adhesive and application thereof

ABSTRACT

A self-adhesive article which is produced by forming an adhesive layer from an adhesive consisting essentially of a polymer which is soluble in or swellable by an iso-thiocyanate, impregnating the adhesive layer with an iso-thiocyanate to provide a biocidal self-adhesive, and applying the biocidal self-adhesive to at lesat one surface of a base material. A high concentration of the iso-thiocyanate can be held in the adhesive layer, and the self-adhesive article is put to uses intended for the purpose of providing bactericidal, fungicidal and microbiocidal effects in building and food-related fields and the like.

TECHNICAL FIELD

The present invention relates to a biocidal self-adhesive comprising anadhesive containing an iso-thiocyanate efficiently held therein to havebacteriostatic, bactericidal and antimicrobial properties and the like,and a process for producing the same, as well as a self-adhesive articlemade by efficiently applying such a self-adhesive onto a support.Particularly, the present invention relates to such a biocidalself-adhesive which can be put to uses widely intended for the purposeof providing bactericidal, fungicidal and microbiocidal effects inbuilding and food-related fields and the like.

The present invention also relates to an iso-thiocyanategradually-releasing sheet, as an application of a self-adhesive articleof the type described above, made by efficiently holding aniso-thiocyanate onto a support such as a paper, a non-woven fabric orthe like through the medium of an adhesive or a low volatile oilyliquid, so that the sheet has antibacterial, bactericidal andantimicrobial properties and the like, and particularly, such anIso-thiocyanate gradually-releasing sheet which can be put to useswidely intended for the purpose of providing bactericidal, fungicidaland microbiocidal effects in various fields such as building,food-related and shoe insole fields.

Further, the present invention relates to a biocidal orfreshness-maintaining self-adhesive sheet, as another application of aself-adhesive article of the type described above, having antibacterialand bactericidal properties and made by efficiently applying an adhesivecontaining an iso-thiocyanate held therein onto a support, and to asterilizing and freshness-maintaining method using such a sheet for thepurpose of providing bactericidal, fungicidal and microbiocidal effectsto a variety of materials to be enclosed by the sheet, including foodproducts such as vegetables and fruits, fresh foods, dried goods andgrains.

BACKGROUND ART

It is known that an iso-thiocyanate contained in a mustard or a wasabi(i.e., Japanese horseradish) have bacteriostatic and bactericidalactions, and any of the synthetic and natural iso-thiocyanates providesbacteriostatic and bactericidal effects even at an extremely smallconcentration of vapor thereof on the order of 10-odd ppm to hundredsppm. Before now, after reporting of this fact, several attempts havebeen made to adsorb the iso-thiocyanate to a porous carrier such as clayminerals or to a surface of a film or a sheet to industrially utilizethe bacteriostatic and bactericidal actions thereof, and a certainarticle made in such a manner, e.g., a freshness maintaining material,has been brought o market.

In the above prior art, however, it is impossible to utilize thebacteriostatic and bactericidal actions of the iso-thiocyanateprofitably. This is because much of the iso-thiocyanate adsorbed inthese methods volatilizes off in the course of production of the articleor during storage of the article, because of its high volatility, andconsequently, an effective amount of iso-thiocyanate cannot be supportedon a carrier. Particularly, when the iso-thiocyanate is adsorbed to aporous carrier, it is necessary to take a measure such that theiso-thiocyanate supported on a porous carrier is placed into a sackhaving a gradually releasing property, because the releasing ratelargely depends upon the temperature. When the iso-thiocyanate isadsorbed to a film or a sheet, there is encountered a problem that it isdifficult to impregnate the film or the sheet with an amount ofiso-thiocyanate sufficient to exhibit an efficacy, but also it isdifficult to control the gradual release.

The freshness maintaining means which has conventionally been used is avacuum pack, or Ageless (Trademark) which is a deoxygenator consistingessentially of active iron oxide, for preventing the oxidation and thepropagation of bacteria. However, with the vacuum pack, a specialapparatus is required, and with the Ageless, it is necessary to pack theAgeless together with a material to be packed. Many food products suchas breads, fishes, meats, box lunches, etc., are only packed with a filmsuch as polyvinylidene chloride and polyethylene (PE) films, or onlyplaced into a container made of a polyvinylidene chloride or apolyethylene. In this case, they are, of course, not durable at roomtemperature and hence, it is necessary to store them, for example, in arefrigerator.

Thereupon, it is conceived to utilize a freshness maintaining materialmade using the iso-thiocyanate, but this is also accompanied by theabove-described problems, resulting in a difficulty to put it topractical use.

DISCLOSURE OF THE INVENTION

The present inventors have repeated zealous studies and as a result, ithas been found that by using, as an adhesive, a polymer soluble in orswellable by an iso-thiocyanate, the iso-thiocyanate can be held in thepolymer by impregnation, with physical properties of the adhesive beingmaintained, thus overcoming the above-described problems.

A biocidal self-adhesive according to the present invention comprises anadhesive impregnated with an iso-thiocyanate to hold the latter therein,the adhesive consisting essentially of a polymer which is soluble in orswellable by the iso-thiocyanate.

A process for producing a biocidal self-adhesive according to thepresent invention comprises the steps of forming an adhesive layer froman adhesive consisting essentially of a polymer which is soluble in orswellable by an iso-thiocyanate, and impregnating the adhesive layerwith the iso-thiocyanate.

Further, a self-adhesive article according to the present invention ismade by applying a biocidal self-adhesive of the type described aboveonto at least one surface of a base material.

Examples of the adhesives consisting essentially of the polymer solublein or swellable by the iso-thiocyanate include acrylic adhesives such ascopolymers of one or more of acrylic and methacrylic esters includingn-butyl acrylate and methacrylate, hexyl acrylate and methacrylate,iso-octyl acrylate and methacrylate, 2-methoxyethyl acrylate andmethacrylate, 2-ethylhexyl acrylate and methacrylate, decyl acrylate andmethacrylate, dodecyl acrylate and methacrylate, tridecyl acrylate andmethacrylate, with a functional monomer which is copolymerizable withsuch esters, such as acrylic, methacrylic, itaconic, maleic andanhydrous maleic acids, hydroxyethyl acrylate, hydroxypropyl acrylate,acrylic amido, dimethylacrylic amido, methylaminoethyl methacrylate, andmethoxyethyl acrylate and methacrylate; vinyl polymer adhesives such asethyl-vinyl ether, propyl-vinyl ether, butyl-vinyl ether and2-ethylhexyl-vinyl ether; and rubber-based adhesives consistingessentially of natural rubbers and synthetic rubbers such asstyrene-isoprene-styrene block terpolymer, styrene-butadiene copolymer,polybutene and butyl rubbers.

The acrylic, rubber-based and vinyl polymer adhesives can be selectivelyused, but it is preferred to selectively use any one of the acrylicadhesives. A particularly preferable adhesive is a copolymer of an alkylacrylate or methacrylate having 4 or more carbon atoms in an alkyl groupand a monomer which is copolymerizable with such ester monomer, and across-linked copolymer is more preferable.

Optionally, other additives may be incorporated into the adhesive,including tackifiers such as terpene and petroleum resins; softenerssuch as liquid paraffin, animal and vegetable oils, e.g., olive, soybeanand bovine oils and lard, polybutene, lower isoprene and was; fillerssuch as titanium oxide, zinc oxide, aluminum metasilicate, calciumsulfate and calcium phosphate; water; emulsifiers such as sorbitanmono-oleate, sodium lauryl sulfonate, emulsifier aids such as magnesiumand aluminum stearates. It should be noted that any of the adhesivesother than those described herein can be used, if they are capable ofbeing dissolved in an iso-thiocyanate or impregnated with aniso-thiocyanate by swelling to hold the iso-thiocyanate therein.

The iso-thiocyanates which can be used are various esters irrespectiveof aliphatic or aromatic type such as the allyl and alkyl esters ofiso-thiocyanic acid, but particularly when the self-adhesive of thepresent invention is intended for food products, it is preferred to usenatural iso-thiocyanate contained in an extract from a mustard and thelike.

The adhesive is preferably impregnated with an iso-thiocyanate to holdthe latter therein at a concentration within a range of 0.1 to 50% byweight based on the adhesive, and desirably to hold the iso-thiocyanatetherein in an amount of 0.1 g/m² or more. In impregnating the adhesivewith an iso-thiocyanate, the iso-thiocyanate may be mixed with a solventor fatty oil having a good compatibility with the adhesive, and theadhesive may be then impregnated with the resulting mixture. The methodfor impregnating the adhesive with the iso-thiocyanate is not limitedand may be a gravure coating and a Mayer bar-coating, as well as a spraycoating, a curtain coating, a stripe coating from a nozzle, animmersion, etc. It is preferable that the impregnating process iscarried out at a temperature of an atmosphere including the adhesivelayer in a range of room temperature or less.

To produce the above-described biocidal self-adhesive, an adhesivepromptly soluble in or swellable by an iso-thiocyanate because of itscompatibility with the latter is applied to a gas-barrier film capableof being a barrier to the iso-thiocyanate, such as an aluminum-coatedpolyethylene terephthalate film, thereby forming an adhesive layer, andimpregnating the adhesive layer with the iso-thiocyanate. This processensures that an amount of iso-thiocyanate which is not available in theprior art process can be supported effectively. It should be noted thatthe gradual releasing of the iso-thiocyanate can be controlled bylaminating a film such as polyethylene and polypropylene films having apermeability to the iso-thiocyanate, to a surface of the adhesive layer.In addition, the iso-thiocyanate can be held for a long period of timeby laminating a gas-barrier film to the surface of the adhesive layer.

The self-adhesive article is basically of such a configuration that thebiocidal self-adhesive is applied to at least one surface of a basematerial, including the above-described configuration. Morespecifically, the self-adhesive article comprises a biocidalself-adhesive supplied to the whole or a portion of one surface oropposite surfaces of a base material such as a resinous film made of apolyethylene terephthalate, a polypropylene, a polyvinyl chloride, apolyethylene, a polycarbonate, a polyvinylidene chloride, apolyacrylonitrile, an ethylene-vinyl alcohol copolymer, etc.; a paper; afabric; a synthetic paper; a metal foil or the like. Usually, a filmtreated with a release agent and having a gas-barrier property ispreliminarily temporarily laminated to the self-adhesive article inorder to protect the adhesive layer. Such a self-adhesive article isreferred to as an adhesive label or an adhesive sheet. It will beunderstood that the article of the present invention includes the formof a so-called adhesive tape made by applying an adhesive layer to onesurface of a base material, while treating the other surface with arelease agent, and rolling the resulting material.

It is as described above that the gradual releasing can be controlled bychanging the gas-barrier property of the base material. It is optionalthat a deposited or coated layer may be provided on the base material,if required.

With the biocidal self-adhesive and the self-adhesive articleimpregnated with the iso-thiocyanate to hold the latter thereinaccording to the present invention, the bacteriostatic, bactericidal,fungicidal, microbiocidal and freshness-maintaining effects possessed bythe iso-thiocyanate can be widely utilized in a variety of fields,because the iso-thiocyanate can be held in the adhesive at a highconcentration and effectively, but also it is possible to utilize thereleasing of the vapor of the iso-thiocyanate without need for a specialapparatus by profitably using an advantage of the adhesive that thearticle can be bonded to all materials. In addition, the use of theprocess comprising the steps of forming the adhesive layer and thenimpregnating the adhesive layer with the iso-thiocyanate ensures thatthe iso-thiocyanate can be held in the adhesive layer at a far higherconcentration, as compared with a process comprising the steps ofpreliminarily incorporating an iso-thiocyanate into an adhesive and thenforming an adhesive layer.

The present inventors have repeated zealous studies for an applicationof the above-described self-adhesive article and as a result, it hasbeen found that the above-described problems are overcome by acombination of an iso-thiocyanate-impermeable barrier sheet and/or aniso-thiocyanate permeation controlling sheet with a self-adhesiveimpregnated with an iso-thiocyanate to hold the latter therein, or aniso-thiocyanate-containing layer formed from a paper or a non-wovenfabric impregnated with an iso-thiocyanate to hold the latter thereinthrough the medium of a low volatility oily liquid.

More specifically, an iso-thiocyanate gradually-releasing sheetaccording to the present invention comprises an iso-thiocyanatesupporting layer which is covered, on its opposite sides, with aniso-thiocyanate-impermeable barrier sheet and/or an iso-thiocyanatepermeation controlling sheet.

In this case, when one side of the layer is covered with the barriersheet and the other side is covered with the controlling sheet, or whenboth the sides are covered with the controlling sheet, the gradualreleasing of the iso-thiocyanate is controlled by the controlling sheet.When both the sides are covered with the barrier sheet, the gradualreleasing of the iso-thiocyanate is controlled by the exposed area ofthe end face of the iso-thiocyanate supporting layer.

The iso-thiocyanate supporting layer is formed by impregnating anadhesive with the iso-thiocyanate to hold the latter therein, or byimpregnating a support such as a paper and a non-woven fabric with theiso-thiocyanate to hold the latter therein through the medium of a lowvolatility oily liquid or the like.

In impregnating the adhesive with the iso-thiocyanate to hold the lattertherein, the adhesive promptly soluble in or swellable by theiso-thiocyanate because of its compatibility with the iso-thiocyanate isapplied to the gas-barrier film such as an aluminum-coated polyethyleneterephthalate serving as a barrier to the iso-thiocyanate, therebyforming an adhesive layer, which is then impregnated with theiso-thiocyanate, and a film permeable to the iso-thiocyanate, such as apolyethylene film, a polypropylene film, an extremely thin polyethyleneterephthalate film, is laminated to adhesive layer, thereby forming aniso-thiocyanate gradually-releasing sheet. This process ensures that anamount of the iso-thiocyanate which is incapable of being supported inthe prior art can be supported effectively.

When the paper or the non-woven fabric is impregnated with theiso-thiocyanate to hold the latter therein through the medium of a lowvolatility oily liquid or the like, the low volatility oily liquid suchas a polybutene containing the iso-thiocyanate dissolved therein isapplied to a non-laminated surface of a paper or a non-woven fabriclaminated, on its side, by an adhesive or by coextrusion, with agas-barrier film serving as a barrier to the iso-thiocyanate, such as analuminum-coated polyethylene terephthalate film, and such surface isfurther laminated with a film permeable to the iso-thiocyanate, such asa polyethylene film formed through an adhesive applying treatment,thereby forming an iso-thiocyanate gradually-releasing sheet. Thisprocess ensures that an amount of the iso-thiocyanate which is incapableof being supported in the prior art can be supported effectively.

Examples of the low volatility oily liquids are a polybutene, acrylicand methacrylic resins having a lower molecular weight, an epoxy resin,mineral oils, animal and vegetable oils such as olive, soybean andbovine oils, liquid paraffin, etc., but any liquids other than thosedescribed herein by way of example can be used, if they have acompatibility with the iso-thiocyanates, cannot react with theiso-thiocyanates and have a fluidity at ambient temperature.

When the iso-thiocyanate supporting layer is formed of an adhesive, itis desirable that the iso-thiocyanate is held in the adhesive byimpregnation at a concentration in a range of 0.1 to 50% by weight basedon the adhesive. Even if the iso-thiocyanate supporting layer is formedof either an adhesive or the paper or the non-woven fabric, it isdesirable that the iso-thiocyanate is held in the adhesive or the paperor the non-woven fabric by impregnation at an amount of 0.1 g/m² ormore.

However, the amount of the iso-thiocyanate is selected depending uponindividual uses and hence, may be out of the above-described range insome cases.

Examples of the iso-thiocyanate-impermeable barrier sheets employed inthe present invention include resinous films such as polyvinylidenechloride, polyacrylonitrile, ethylene-vinyl alcohol copolymer,polyethylene terephthalate and polycarbonate films; metal foils and thelike. Examples of the iso-thiocyanate permeation controlling sheetsinclude resinous films such as polyethylene, polypropylene and polyvinylchloride films, papers, fabrics and synthetic papers. Even with thebarrier sheet, the permeability thereof can be varied by reducing thethickness of a film and thus, such a barrier sheet can be also used as acontrolling sheet.

The iso-thiocyanate-impermeable barrier sheet and theiso-thiocyanate-permeation controlling sheet may be used as a singlelayer structure or as a different sheet-laminated structure.

The iso-thiocyanates and the adhesives soluble in or swellable by theiso-thiocyanates which can be used are those described above for theadhesive article.

The iso-thiocyanate gradually-releasing sheet according to the presentinvention is capable of holding the iso-thiocyanate therein at a highconcentration and effectively by the above-described configuration, butalso capable of controlling the releasing of the vapor of theiso-thiocyanate by selection of the film.

Further, the present inventors have repeated zealous studies for anotherapplication of the above-described adhesive article and as a result,have overcome the problems in the prior art freshness maintaining meansby utilizing the above-described knowledge that by using, as anadhesive, a polymer soluble in or swellable by an isothiocyanate, theiso-thiocyanate can be held in the polymer by impregnation, withphysical properties of the adhesive being maintained.

More specifically, a self-adhesive sheet according to the presentinvention for sterilizing a material to be packed and maintaining thefreshness of the material comprises an adhesive layer 2 impregnated withan iso-thiocyanate to hold the latter therein and mounted on a basesheet 1 having a low permeability to the iso-thiocyanate, as comparedwith a packing material for a material to be packed, as shown in FIG. 1.

In the self-adhesive sheet shown in FIG. 1, used as a base sheet 1 was asheet which includes an aluminum-coated film 1b on one side of apolyethylene terephthalate (PET) film 1a and which has littlepermeability to iso-thiocyanates. In FIG. 1, reference numeral 3designates an iso-thiocyanate-barrier release sheet including asilicone-treated release layer 3b on one side of a PET film 3a.

The self-adhesive sheet for sterilizing a material to be packed andmaintaining the freshness of the material is selected depending upon therelative relationship with a packing material, but it is preferable thata base material having a total iso-thiocyanate-barrier property is used.Such materials include polymers such as a polyethylene terephthalate, apolycarbonate, a polyvinylidene chloride, a polyacrylonitrile and anethylene-vinyl alcohol copolymer, and metal foils.

With the above-described sterilizing and freshness-maintainingself-adhesive sheet, the types of the adhesive and the iso-thiocyanate,the amount and method of impregnation of the iso-thiocyanate in adhesiveand the self-adhesive sheet producing process are the same as thosedescribed above for the self-adhesive article and hence, the descriptionthereof is not repeated here.

A method for sterilizing and freshness-maintaining a material to bepacked according to the present invention comprises affixing aself-adhesive sheet of the type described above to an outer surface of apacking material for a material to be packed.

Thus, it is possible to sterilize the material to be packed and tomaintain the freshness of such material, without destruction of thepacking material. The packing material is not limited in any way, andany compositions can be used, if they have a lower barrier effect toiso-thiocyanates than that of the self-adhesive base material.

The extremely appropriate sterilization and freshness-maintaining can beperformed by selecting the size of the self-adhesive sheet, the affixingplace, the affixing time and the amount of iso-thiocyanate held byimpregnation.

According to the present invention, the freshness-maintainingbactericidal and fungicidal effects and the like for food products canbe widely utilized, because the above-described means makes it possibleto release the vapor of the iso-thiocyanate through the packing materialto the content in the packing material such as food products withoutneed for a special apparatus by profitably using an advantage of theadhesive that the article and sheet can be bonded to all materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a biocidal self-adhesive sheet forsterilizing a material to be packed and maintaining the freshness of thematerial according to the present invention;

FIG. 2 is a graph illustrating the iso-thiocyanate releasingcharacteristic of a biocidal self-adhesive according to the presentinvention;

FIG. 3 is a diagram illustrating one embodiment of an iso-thiocyanategradually-releasing sheet according to the present invention;

FIG. 4 is a diagram illustrating another embodiment of aniso-thiocyanate gradually-releasing sheet according to the presentinvention; and

FIG. 5 is a diagram illustrating a further embodiment of aniso-thiocyanate gradually-releasing sheet according to the presentinvention.

THE BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail by way ofparticular examples, but is not limited to these examples in any way.

EXAMPLE 1

There was prepared an ethyl acetate solution containing 40% by weight ofa copolymer formed of 97% by weight of 2-ethylhexyl acrylate and 3% byweight of acrylic acid. An isocyanate-based cross-linking agent wasadded in an amount of 1% by weight to the solution, and the mixture wasapplied onto an aluminum-coated polyester film. The resulting materialwas dried for 2 minutes at 100° C., thus producing an self-adhesivesheet with its adhesive layer having a thickness of 30 μm. Further, theadhesive layer was impregnated with a stock solution of an allyliso-thiocyanate at room temperature, thereby preparing a self-adhesivesheet containing 10% by weight of the allyl iso-thiocyanate in theadhesive. An aluminum-coated polyester film treated on one side with asilicone was laminated to the self-adhesive sheet to provide aself-adhesive article having a release film thereon.

EXAMPLE 2

A self-adhesive article having a release film thereon was produced inthe same manner as in Example 1, except that 0.1% by weight of the allyliso-thiocyanate was contained in the adhesive.

EXAMPLE 3

A self-adhesive article having a release film thereon was produced inthe same manner as in Example 1, except that 25% by weight of the allyliso-thiocyanate was contained in the adhesive.

EXAMPLE 4

A self-adhesive article having a release film thereon was produced inthe same manner as in Example 1, except that 50% by weight of the allyliso-thiocyanate was contained in the adhesive.

EXAMPLE 5

Dissolved in toluene were 100 parts of a styrene-isoprene-styrene blockcopolymer (Califlex TR1107 made by Shell Chemistry Corp.), 60 parts ofliquid paraffin and 150 parts of a tackifier (Alcon P100 made by ArakawaChemistry K.K.). The resulting solution was applied to analuminum-coated polyester film, and dried for 2 minutes at 100° C.,thereby producing a self-adhesive sheet with its adhesive layer having athickness of 30 μm. Further, the adhesive layer was impregnated with astock solution of an allyl iso-thiocyanate at room temperature, therebypreparing a self-adhesive sheet containing 5% by weight of the allyliso-thiocyanate. An aluminum-coated polyester film treated on one sidewith a silicone was laminated to the self-adhesive sheet to provide aself-adhesive article having a release film thereon.

EXAMPLE 6

A solution of 2-ethylhexyl-acrylate acrylic acid copolymer in ethylacetate, prepared in the same manner as in Example 1, was applied onto arelease surface of an aluminum-coated polyester film having one sidetreated with a release agent, and was then dried for 2 minutes at 100°C. thereby producing a self-adhesive sheet with its adhesive layerhaving a thickness of 25 μm. This sheet was laminated to a non-wovenfabric. Further, an adhesive layer having a thickness of 25 μm wasseparately formed on a release surface of an aluminum-coated polyesterfilm treated on one side with a release agent, and was impregnated withan allyl iso-thiocyanate at room temperature. The non-woven fabric sideof the self-adhesive sheet/non-woven fabric laminate and the adhesiveside of the self-adhesive sheet impregnated with the allyliso-thiocyanate were laminated to each other, thereby providing adouble-sided self-adhesive article containing 10% by weight of the allyliso-thiocyanate.

Comparative Example 1

Using a silicone adhesive, an adhesive layer of 30 μm was formed on analuminum-coated polyester film,, and a stock solution of an allyliso-thiocyanate was applied to the adhesive layer to provide aself-adhesive sheet. This sheet is laminated to an aluminum-coated filmtreated on one side with a fluorine-based release agent, therebyproviding a self-adhesive article having a release film laminated to thealuminum-coated film.

Comparative Example 2

A double sided self-adhesive article was produced in the same manner asin Example 6, except that the adhesive layer was impregnated with noallyl iso-thiocyanate.

Then, the adhesion (according to JIS Z0237) was measured for theself-adhesive articles produced in Examples 1 to 5 and ComparativeExample 1, thereby providing results as given in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                   Adhesion (g/25 mm, against SUS)                                    ______________________________________                                        Example                                                                       1              900                                                            2            1,200                                                            3              650                                                            4              160                                                            5            1,350                                                            Comparative Example                                                           1               0                                                             ______________________________________                                    

As apparent from Table 1, it can be seen that each of the self-adhesivearticles produced in Examples 1 to 5 has an adhesion property, even ifthe allyl iso-thiocyanate is contained therein at a high concentration,and this enables the formation of a sheet from these articles, theaffixing thereof to an object and the lamination thereof. In contrast,it can be seen that when the silicone adhesive insoluble in orunswellable by the allyl iso-thiocyanate is used as the adhesive, theresulting article has no adhesion property, because the allyliso-thiocyanate remains as liquid on the surface of the adhesive and thesurface of the release film.

The % residue of the allyl iso-thiocyanate, when the self-adhesivearticle having the release film and produced in Example 1 was left tostand at room temperature, was measured to provide results as given inTable 2.

                  TABLE 2                                                         ______________________________________                                        Residue                                                                       Lapse of time (day)                                                           Example after 1 day                                                                             after 3 days                                                                            after 7 days                                                                          after 15 days                             ______________________________________                                        1       99.3      99.0      98.2    96.7                                      ______________________________________                                    

As apparent from Table 2, it can be seen that even if the self-adhesivearticle is left to stand at room temperature, the volatilization of theallyl iso-thiocyanate can be reduced to the minimum by the fact that theself-adhesive article assumes the form as in Example 1.

Then, using the double-sided self-adhesive articles produced in Example6 and Comparative Example 2, two veneers each having a thickness of 5 mmwere laminated thereto. The resulting laminates were left to stand in a70% Rh atmosphere at 25° C., and the propagation of fungi thereon wasobserved with the lapse of time. As a result, when the double sidedself-adhesive article produced in Example 6 was used, little generationof fungi was observed even after one month, whereas when the doublesided self-adhesive article produced in Comparative Example 2 was used,fungi were generated on a portion of the laminate after one week, andthe fungi were spread over substantially the entire surface of thelaminate after two weeks.

Then, the release film of each of the self-adhesive articles having therelease film and produced in Examples 1, 3 and 4 was peeled off and leftto stand in a 500 cm³ stainless container, so that the adhesive surfacecannot come into contact with an inner wall of the container. Theconcentration of the allyl iso-thiocyanate in the container was measuredwith the lapse of time by a gas chromatography. The result showed thateach of the self-adhesive articles released the allyl iso-thiocyanaterapidly, so that the concentration of the allyl iso-thiocyanate in thesealed container was kept constant, as shown in FIG. 2.

EXAMPLE 7

There was prepared an ethyl acetate solution containing 40% by weight ofa copolymer formed of 97% by weight of 2-ethylhexyl acrylate and 3% byweight of acrylic acid. An iso-cyanate-based cross-linking agent wasadded in an mount of 1% by weight to the solution. The resulting mixturewas applied to a polyester film having a thickness of 3 μm and dried forone minute at 100° C. to form an adhesive layer of 30 μm. Then, an allyliso-thiocyanate was applied to the adhesive layer in a room temperaturecondition by a gravure coating (using a gravure mesh: Lattice 120 Meshmade by Asahi Roll, Corp.), so that the allyl iso-thiocyanate wascontained in the adhesive layer. The resulting film was laminated to apolyethylene film having a thickness of 50 μm to produce an allyliso-thiocyanate containing sheet.

EXAMPLE 8

An acrylic adhesive layer of 30 μm was formed on a polyester film havinga thickness of 38 μm in the same manner as in Example 7. Then, using aMayer bar, the adhesive surface was coated with an allyliso-thiocyanate, so that the allyl iso-thiocyanate was contained in theadhesive layer. The resulting film was laminated to a polyester filmtreated with a release agent and having a thickness of 38 μm to providea self-adhesive sheet containing the allyl iso-thiocyanate.

Comparative Example 3

An iso-cyanate-based cross-linking agent was added in an amount of 1% byweight to an ethyl acetate solution containing 40% by weight of acopolymer formed of 97% by weight of 2-ethylhexyl acrylate and 3% byweight of acrylic acid, and an allyl iso-thiocyanate was added to thesolution in an amount of 20 parts by weight per 100 parts of thesolution. The resulting mixture was applied to a polyester film having athickness of 38 μm and dried for 1 minute at 80° C. to form an adhesivelayer of 30 μm. The resulting film was laminated to a polyethylene filmhaving a thickness of 50 μm to provide an allyl iso-thiocyanatecontaining sheet.

Comparative Example 4

Added to an emulsion solution containing 65% by weight of a copolymerformed of 97% by weight of 2-ethylhexyl acrylate and 3% by weight ofacrylic acid was an allyl iso-thiocyanate in an amount of 32.5 parts byweight per 100 parts by weight of the solution. The resulting mixturewas applied to a polyester film having a thickness of 38 μm and driedfor 1 minute at 80° C. to form an adhesive layer of 30 μm. The resultingfilm was laminated to a polyester film treated with a release agent andhaving a thickness of 38 μm to provide an allyl iso-thiocyanatecontaining sheet.

Then, the content of each of the allyl iso-thiocyanates in Examples 7and 8 and Comparative Examples 3 and 4 was measured to provide resultsas given in Table 3.

The content was determined by cutting a sample sheet into a piece havinga size of 20 cm×10 cm, leaving the cut piece to stand in an atmosphereat 40° C. under 10 Torr for 48 hours using a vacuum drier, removing theallyl iso-thiocyanate, and finding the content from the resultingvariation in weight and the amount of adhesive applied.

                  TABLE 3                                                         ______________________________________                                                   Content of allyl iso-thiocyanate (%)                               ______________________________________                                        Example                                                                       7            19.19                                                            8            28.26                                                            Comparative Example                                                           3            0.11                                                             4            0.23                                                             ______________________________________                                    

EXAMPLE 9

An acrylic adhesive layer 11 containing 20% by weight of an allyliso-thiocyanate was formed on a deposited surface 10a of analuminum-coated polyethylene terephthalate film 10 having a thickness of25 μm, as shown in FIG. 3. The resulting film and a polyethylene film 12having a thickness of 60 μm were laminated to each other to provide agradually releasing sheet.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about one hour at a releaserate of 10.6 g/m².hr.

EXAMPLE 10

A gradually releasing sheet was produced in the same manner as inExample 9, except that the polyethylene in Example 9 was replaced by apolyethylene terephthalate film having a thickness of 16 μm.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about 36 hours at a releaserate of 0.28 g/m².hr.

EXAMPLE 11

A gradually releasing sheet was produced in the same manner as inExample 9, except that the polyethylene in Example 9 was replaced by apolyethylene terephthalate film having a thickness of 50 μm.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about 105 hours at a releaserate of 0.09 g/m².hr.

EXAMPLE 12

A gradually releasing sheet was produced in the same manner as inExample 9, except that the polyethylene in Example 9 was replaced by apolypropylene film having a thickness of 60 μm.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about 12 hours at a releaserate of 0.83 g/m².hr.

EXAMPLE 13

A gradually releasing sheet was produced in the same manner as inExample 9, except that the polyethylene in Example 9 was replaced by analuminum-deposited polyethylene terephthalate film having a thickness of25 μm.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about 2900 hours at arelease rate of 0.003 g/m².hr.

EXAMPLE 14

An acrylic adhesive layer 21 containing 20% by weight of an allyliso-thiocyanate was formed on a coated surface 20a of an aluminum-coatedpolyethylene terephthalate film 20 having a thickness of 25 μm, as shownin FIG. 4. The film was laminated to a wood free paper 22 (KonywrapWhite 100 g/m² made by Lintec Corp.). The adhesive surface of a sheetcomprising an acrylic adhesive layer 24 formed on a polyethylene film 23having a thickness of 60 μm was laminated to the paper surface of theresulting laminate to provide a gradually releasing sheet having anerve.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about one hour at a releaserate of 9.5 g/m².hr.

EXAMPLE 15

An acrylic adhesive layer 31 was formed on a coated surface 30a of analuminum-coated polyethylene terephthalate film 30 having a thickness of25 μm, as shown in FIG. 5. The film was laminated to a paper 32 (Linterpaper LCL-145 made by Taihei Paper Co., Ltd.) to prepare a laminate 33.

Then, an allyl iso-thiocyanate was dissolved in a polybutene (NissekiPolybutene HV-100 made by Nippon Oil Co., Ltd.), so that theconcentration of the allyl iso-thiocyanate was 5% by weight. Thissolution of allyl iso-thiocyanate in the polybutene was applied to thepaper surface of the laminate 33, and then, an adhesive surface of asheet having an acrylic adhesive layer 35 formed on a polyethyleneterephthalate film 34 having a thickness of 25 μm was laminated to thecoated surface of the laminate 33 to provide a gradually releasingsheet.

The releasing of the allyl iso-thiocyanate was examined, and the resultshowed that the releasing was sustained for about 60 hours at a releaserate of 0.14 g/m².hr.

EXAMPLE 16

A self-adhesive sheet was produced, in accordance with the configurationshown in FIG. 1, by permitting an allyl iso-thiocyanate to be containedin an amount of 10% by weight in a self-adhesive article which was madeby adding an iso-cyanate-based cross-linking agent in an amount of 1% byweight to a copolymer acrylic adhesive formed of 97% by weight of2-ethylhexyl acrylate and 3% by weight of acrylic acid. A loaf of breadand boiled rice were placed into a polyethylene sack (20 mm×85 mm×0.08mm) which was then sealed. Subsequently, the self-adhesive sheet was cutinto a piece having a size of 2 cm×2 cm, and the release sheet waspeeled off from the cut piece. The resulting sheet was affixed to thepolyethylene sack from the outside. This sack was left to stand at roomtemperature. After two weeks, with regard to the loaf of bread, novariation was observed, and with regard to the boiled rice, a moisturecondensation was only observed on an inner surface of the sack.

As a control, a loaf of bread and boiled rice were placed into apolyethylene sack which was then sealed, in the same manner as inExample 16. This sack was left to stand at room temperature withoutaffixing of the self-adhesive sheet thereto. After about 5 days, fungiwere developed on the loaf of bread, and after 10 days, these fungi werespread over substantially the entire surface of the loaf of bread. Withregard to the boiled rice, on the other hand, fungi were developedthereon after 4 days, and the rice was rotted to have no trace oforiginal form after 10 days.

EXAMPLE 17

A self-adhesive sheet similar to that in Example 16 was cut into a pieceof 5 cm×5 cm, and the release sheet was peeled off therefrom. Then, thecut piece was affixed to a central portion of an outer surface of apolyethylene package of each of three packs of boiled noodles. Inaddition, three packs of boiled noodles with no self-adhesive sheetaffixed thereto were prepared as a control. The six packs in total werestored at room temperature, and after 7 days, variations in freshnessthereof were compared.

The result of observation was as given in Table 4. A distinctfreshness-maintaining effect due to the affixing of the allyliso-thiocyanate containing self-adhesive sheet was observed, as given inTable 4.

                  TABLE 4                                                         ______________________________________                                                   Result of observation                                                         change of color                                                                           Foul smell                                                          After   after     after after                                    Sample       3 days  7 days    3 days                                                                              7 days                                   ______________________________________                                        group with   0/3      1/3*     0/3   0/3                                      self-adhesive                                                                 sheet affixed                                                                 Control group                                                                              1/3     3/3       2/3   3/3                                      ______________________________________                                         *change of color extremely in part                                       

EXAMPLE 18

Twelve small rice cake packs each placed into a polyethylene sack weredivided into four groups each comprising three rice cake packs. Onegroup was used as a control (untreated), and with regard to the threeother groups, an allyl iso-thiocyanate containing self-adhesive sheetsimilar to that in Example 16 was affixed to a central portion of awrapping film of each group under conditions given in Table 5.

                  TABLE 5                                                         ______________________________________                                                          Size of self-                                               Test No.          adhesive sheet (cm.sup.2)                                   ______________________________________                                        (1)               3                                                           (2)               5                                                           (3)               7                                                           (4)               0      (Control)                                            ______________________________________                                    

Each sample was stored for long time at room temperature, and the testwas carried out for the following items:

1) The condition of fungi developed: after 1 day, 3 days and 7 days fromthe affixing

2) The remaining odor of mustard: after 1 day and 7 days from theaffixing

The test results were as given in Table 6.

                  TABLE 6                                                         ______________________________________                                        Test result                                                                                       Remaining                                                 Test  Appearance          mustard odor**                                      group after     after   after   after after                                   No.   1 day     3 days  7 days  1 day 7 days                                  ______________________________________                                        1     -         -       ±    ±  -                                       2     -         -       ±    +     -                                       3     -         -       -       +     -                                       4     -         ±    +                                                     (control)                                                                     ______________________________________                                         *Judgment of the appearance is as follows:                                    +Fungi were developed over substantially the entire region                    ±Fungi were developed in part                                              -There was no change                                                          **Criterion of judgment is as follows:                                        +There was no odor of mustard                                                 ±There was a little odor of mustard                                        -There was no odor of mustard                                            

In the group with the allyl iso-thiocyanate containing self-adhesivesheet affixed, the development of fungi was inhibited in proportion tothe size of the sheet. On the other hand, the odor of mustard was sensedin all of the groups (1) to (3) after 1 day, but was reduced after 7days to such an extent that it could not be already sensed, whichindicates the odor of this degree has little effect on the food taste.

Possibility of Industrial Application

With the biocidal self-adhesive and the process for producing the sameaccording to the present invention, the iso-thiocyanate can be supportedat a high concentration and moreover, the self-adhesive article can beproperly affixed to a desired place in any form such as sheet, tape andlabel forms by utilization of the adhesion property of the adhesive,thereby effectively utilizing the bacteriostatic, bactericidal andmicrobiocidal properties of the iso-thiocyanate.

In the prior art methods for incorporating the iso-thiocyanate inclathration to a cyclodextrin and for adsorbing the iso-thiocyanate to aporous carrier such as a clay mineral, a slight amount of theiso-thiocyanate is merely contained in the final form of the sheet, butalso the cost of the sheet is very high. In contrast, with theiso-thiocyanate gradually-releasing sheet of the present invention, alarge amount of the iso-thiocyanate can be contained in the sheet andfurther, the gradual releasing of the iso-thiocyanate is possible. Inaddition, the cost can be minimized, leading to an inexpensive article.

In the case of the prior art vacuum pack and Ageless (Trademark), it isnecessary to conduct the packing in the packing line together with thematerial to be packed, and sealability and air-tightness are requiredfor packing. In contrast, with the self-adhesive sheet for sterilizingthe material to be packed and for maintaining the freshness of thematerial to be packed according to the present invention, even if asmall amount of the iso-thiocyanate is leaked, the iso-thiocyanate isreplenished from the self-adhesive sheet. Therefore, the sterilizing andfreshness-maintaining effects can be exhibited sufficiently, even if theair-tightness is small. Further, the time for affixing of the sheet neednot necessarily be in the manufacture line, and even if the sheet isaffixed after buying of a food product by a general purchaser, the sameeffect is obtained.

What is claimed is
 1. An iso-thiocyanate gradually releasing sheetcomprising:(a) an iso-thiocyanate supporting layer which comprises anadhesive impregnated with an iso-thiocyanate in an amount of 0.1 to 50%by weight of said adhesive; (b) a barrier sheet covering one side ofsaid iso-thiocyanate supporting layer, said barrier sheet beingimpermeable to iso-thiocyanate; and (c) an iso-thiocyanate permeationcontrolling sheet covering said iso-thiocyanate supporting layer on theside opposite to the side covered by the barrier sheet, saidiso-thiocyanate permeation controlling sheet being permeable to thevapor of said iso-thiocyanate.
 2. An iso-thiocyanate gradually releasingsheet as in claim 1, wherein said adhesive consists essentially of apolymer which is soluble in or swellable by said iso-thiocyanate.
 3. Aniso-thiocyanate gradually releasing sheet as in claim 2, wherein saidpolymer is a copolymer of a first monomer which is an alkyl acrylate oran alkyl methacrylate, wherein the alkyl group has at least 4 carbonatoms, and a second monomer which is copolymerizable with the firstmonomer.
 4. An iso-thiocyanate gradually releasing sheet as in claim 1,wherein said barrier sheet is a laminate of at least two layers.
 5. Aniso-thiocyanate gradually releasing sheet as in claim 1, wherein saidiso-thiocyanate permeation controlling sheet is a laminate of at leastof two layers.
 6. An iso-thiocyanate gradually releasing sheetcomprising:(a) an iso-thiocyanate supporting layer which comprises apaper or a non-woven fabric which is impregnated with an iso-thiocyanatein a medium of an oily liquid having low volatility, wherein the amountof iso-thiocyanate is at least 0.1 g/m² ; (b) a barrier sheet coveringone side of said iso-thiocyanate supporting layer, said barrier sheetbeing impermeable to iso-thiocyanate; and (c) an iso-thiocyanatepermeation controlling sheet covering said iso-thiocyanate supportinglayer on the side opposite to the side covered by the barrier sheet,said iso-thiocyanate permeation controlling agent being permeable to thevapor of said iso-thiocyanate.
 7. An iso-thiocyanate gradually releasingsheet as in claim 6, wherein said barrier sheet is a laminate of atleast two layers.
 8. An iso-thiocyanate gradually releasing sheet as inclaim 6, wherein said iso-thiocyanate permeation controlling sheet is alaminate of at least two layers.
 9. An iso-thiocyanate graduallyreleasing sheet comprising:(a) an iso-thiocyanate supporting layer whichcomprises an adhesive impregnated with an iso-thiocyanate in an amountof 0.1 to 50% by weight of said adhesive; (b) a first barrier sheetcovering one side of said iso-thiocyanate supporting layer, said barriersheet being impermeable to said iso-thiocyanate; and (c) a secondbarrier sheet covering said iso-thiocyanate supporting layer on the sideopposite to the side covered by the first barrier sheet.
 10. Aniso-thiocyanate gradually releasing sheet as in claim 9, wherein saidadhesive consists essentially of a polymer which is soluble in orswellable by said iso-thiocyanate.
 11. An iso-thiocyanate graduallyreleasing sheet as in claim 10, wherein said polymer is a copolymer of afirst monomer which is an alkyl acrylate or an alkyl methacrylate,wherein the alkyl group has at least 4 carbon atoms, and a secondmonomer which is copolymerizable with the first monomer.
 12. Aniso-thiocyanate gradually releasing sheet as in claim 9, wherein saidbarrier sheet is a laminate of at least two layers.
 13. Aniso-thiocyanate gradually releasing sheet comprising:(a) aniso-thiocyanate supporting layer which comprises a paper or a non-wovenfabric which is impregnated with an iso-thiocyanate in a medium of anoily liquid having low volatility, wherein the amount of iso-thiocyanateis at least 0.1 g/m² ; (b) a first barrier sheet covering one side ofsaid iso-thiocyanate supporting layer, said barrier sheet beingimpermeable to said iso-thiocyanate; and (c) a second barrier sheetcovering said iso-thiocyanate supporting layer on the side opposite tothe side covered by the first barrier sheet.
 14. An iso-thiocyanategradually releasing sheet as in claim 13, wherein said barrier sheet isa laminate of at least two layers.
 15. An iso-thiocyanate graduallyreleasing sheet comprising:(a) an iso-thiocyanate supporting layer whichcomprises an adhesive impregnated with an iso-thiocyanate in an amountof 0.1 to 50% by weight of said adhesive; (b) a first iso-thiocyanatepermeation controlling sheet covering one side of said iso-thiocyanatesupporting layer; and (c) a second iso-thiocyanate permeationcontrolling sheet covering said iso-thiocyanate supporting layer on theside opposite to the side covered by the first iso-thiocyanatepermeation controlling sheet, wherein the first and secondiso-thiocyanate permeation controlling sheets are permeable to the vaporof said iso-thiocyanate.
 16. An iso-thiocyanate gradually releasingsheet as in claim 15, wherein said adhesive consists essentially of apolymer which is soluble in or swellable by said iso-thiocyanate.
 17. Aniso-thiocyanate gradually releasing sheet as in claim 16, wherein saidpolymer is a copolymer of a first monomer which is an alkyl acrylate oran alkyl methacrylate, wherein the alkyl group has at least 4 carbonatoms, and a second monomer which is copolymerizable with the firstmonomer.
 18. An iso-thiocyanate gradually releasing sheet as in claim15, wherein said iso-thiocyanate permeation controlling sheet is alaminate of at least two layers.
 19. An iso-thiocyanate graduallyreleasing sheet comprising:(a) an iso-thiocyanate supporting layer whichcomprises a paper or a non-woven fabric which is impregnated with aniso-thiocyanate in a medium of an oily liquid having low volatility,wherein the amount of iso-thiocyanate is at least 0.1 g/m² ; (b) a firstiso-thiocyanate permeation controlling sheet covering one side of saidiso-thiocyanate supporting layer; and (c) a second iso-thiocyanatepermeation controlling sheet covering said iso-thiocyanate supportinglayer on the side opposite to the side covered by the firstiso-thiocyanate permeation controlling sheet, wherein the first andsecond iso-thiocyanate permeation controlling sheets are permeable tothe vapor of said iso-thiocyanate.
 20. An iso-thiocyanate graduallyreleasing sheet as in claim 19, wherein said iso-thiocyanate permeationcontrolling sheet is a laminate of at least two layers.